Method and material for preventing the tarnishing of silverware



Patented-June 24, 1930 UNITED STATES PATEN'D OFFICE GRINNELL JOKES, OF CAMBRIDGE, MASSACHUSETTS, ASSIGNOB TO PACIFIC MILLS, OE

LAWRENCE, MASSACHUSETTS, A. CORPORATION OF MASSACHUSETTS METHOD AND MATERIAL FOR PREVENTING THE TARNISHING OE SILVERWARE Io Drawing.

Silverware will tarnish in a short time merely from exposure to ordinary atmosphere even if wrapped in bags and packed in closed drawers or trunks as usual. When stored for the summer or other extended period in safe deposit vaults, or elsewhere,

silverware usually becomes coated with a tarnish so thick and adherent that cleaning is a long task. In the case of silverware elaborately embossed or engraved, complete cleaning is impossible by ordinary meanspreventing the tarnishing of silver and the.

wasteful cycle of polishing, storing and repolishing silver by preventing the formation of the tarnish.

The air and dust particles, especially in cities, contain minute traces of sulphur and sulphur compounds such as hydrogen sulphide or sulphur dioxide. Silver has such a very great chemical afiinity for sulphur that it is capable of extracting these minute traces of sulphur from the air or from dust particles with the formation of silver sulphide and thereby becomes tarnished.

Some of the attempts to protect silver against tarnishing have been based on the idea of making agas-tight container to prevent access of sulphur fumes to the silver. But such containers are cumber. some and awkward and permit access of sulphur fumes to the silver every time the container is opened to replace the silver articles so that they are only partially; effective. 1

Another method which is use is to cover the silverware with a transparent lacquer.

Application filed July 11,

1929. Serial No. 377,629.

Although such lacquers are partially successful in preventing tarnish, they'cannot be used on table ware because the lacquers will not stand the wear and washing to which they must be subjected.

It has also been suggested that the silverware should be wrapped in a bag impregnated with chemicals which dissolve or decompose silver sulphide so that the silverware when withdrawn will be free from 60,

tarnish. A bag impregnated with potassium ferrocyanide, potassium cyanide and glycerine has been suggestedfor this purpose. Potassium cyanide is an excellent solvent for silver sulphide and is, therefore, effective in detarnishing'silver, but owing to the extremely poisonous nature of potassium cyanide,- such a bag could not be used safely in the home and such a bag would soon lose any effectiveness it might have owing to the instability of potassium cyanide when exposed to air containing even traces of carbon dioxide. tion of this idea is to impregnate a paper with metallic zinc which in the presence of moisture and a soluble electrolyte is capable of decomposing silver sulphide.

Other attempts have been based on theidea that a cloth may be treated with a substance which will absorb and combine with the sulphur or sulphur compounds in the-air and thus protect silverware enclosed within the treated cloth. Among the substances which have been suggested for this purpose are the oxide of lead, oxide of zinc, oxide of iron, borax,'caustic alkalies, acetate of zinc, and chloride of zinc. I have found by repeated and careful experiments that although some of these substances will combine with and absorb sulphur compounds, the protection whichthey give is imperfect and temporary. I have also tried many other substances Another variawhich, so far as I am aware, have never been used for this purpose and which are capable of forming insoluble sulphides, In-

eluding cadmium, bismuth, copper and antimony in the form of metal, or oxides or salts and find thatalthough a cloth impregnated with these substances will give some temporary protection to silverware enclosed therein, the protection is imperfect and too short-lived to give satisfaction to the purchaser of such a cloth. The difliculty with all of these substances is that silver has a much greater chemical afiinity for sulphur than any of the materials hitherto used to impregnate the cloth so that the sulphur will be passed on by the impregnating materials to the silverware in contact with the cloth, especially if the cloth is slightly moist.

I have found by extended experiments not only with the metals above described but with many other metals that this transfer takes place. The attraction of silver for sulphur exceeds that of all other usable metals so that silverware should tarnish in time from contact with the sulphide of any other usable metal. I have found, however, that if silver (or silver oxide or other salt of silver which will form silver sulphide, when exposed to the usual atmosphere or dust containing sulphur) is precipitated on or preferably throughout a bag or other wrapping and the bag or wrapping is placed around silverware that the silverware will not tarnish. I believe that the silver or silver salt in its finely divided. state unites more readily with sulphur than does a solid block of silver, as a-spoon, and that the finely divided silver, or silver compound, when once united with the sulphur will not pass the sulphur along to the silverware to be protected. Thus I have found sterling silver in bags in which silver or silver oxide has been precipitated will gave protection for sixteen months and probably much more. The above statement of the reasons for the success of mybags I believe to be true but whatever the cause, the fact is that ha s impregnated according to my invention 0 give long protection which bags impregnated with other materials do not. 7

I deposit the silver or silver compound which acts as a sulphur absorbent on .the cloth in finely divided but solid, insoluble, and adherent form which leaves thelcloth in a soft and pliable condition and attractive in appearance and feel. I prefer to use a napped cotton cloth of close weave so that the interstices shall, be a minimum, but fabrics of other materials or of other construction may be used, such as paper or felt.

To prepare a silver protecting cloth in accordance with-my invention, I take a suitable napped cotton cloth and pass it through a solution containing twelve ounces of silver nitrate dissolved in a gallon of water and then pass the cloth through a squeeze roll or wringer to remove the excess of silver nitrate solution. Then without drying the cloth, I pass it into a hot alkaline solution of sodium carbonate containing 2% of sodium carbonate, thereby causing the silver to be precipitated on and in the cotton and that the procedure may be. varied with- V out departing from the spirit of my invention. Thus, by using a weaker solution of silver nitrate the cost of the cloth will be reduced with some diminution of the length of time that the cloth will give perfect protection. Other soluble silver salts can be used instead of silver nitrate. The concentration of the sodium carbonate solution and the time and temperature of the treatment of the cloth with the sodium carbonate solution may be Varied within wide limits. Other precipitating reagents may be used instead of sodium carbonate. Reducing agents which will change the silver compounds to metallic silver in whole or in part may be used if desired. Formaldehyde is suitable for this purposealthough other reducing agents'may be used if desired.

The term impregnated includes surface impregnation except where limited bythe context.

Silver in any combination which will combine freely with sulphur as itoccurs in the atmosphere or dust on exposure under ordinary conditions, is included in my invention as an impregnating material.

I have used the term silver constituent in the claims to include metallic silver or suitable compounds thereof and also mixtures of silver with suitable silver compounds. Some silver compounds would attack the hands of the user or poison the user or destroy the bags and would obvifurther chemical treatment.

In this specification I have described my preferred method of impregnation by. precipitating a suitable compound practically insoluble in water in the fabric. This method I have found to have many advantages. A material impregnated with a comound insoluble in water in finely divided orm may be washed without loss of material and presents a very large surface for contact with the tarnishing gases or dust while a fabric treated with a water soluble salt of silver without further treatment is almost certain to crystallize and when it unites with sulphur will usually produce an acidwhich is highly undesirable. Nevertheless, some protection is given even by impregnation with suitable soluble salts of silver. V

In view of the expense of the silver impregnated cloth, and the selling advantage of variety of color in the wrappers, it will often be desirable to make impregnated pockets fitted to hold one or more articles of silverware and wrap the pockets containing the silver in an unimpregnated wrapper.

If for any reason it is desired to produce a bag of a color which cannot be produced by a complete impregnation according to my invention, a surface impregnation on one side of the cloth only may be used and will result in material protection.

I claim: I 1. A fabric for protecting silverware from tarnish comprising a material suitable for wrapping, impregnated with a silver constituent in a combination or condition which will combine with the tarnishing gases in the atmosphere accessible to the silverware wrapped therein.

2. A fabric for protecting silverware from- 5 tarnish comprising a material suitable for wrapping, impregnated with a silver constitutent insoluble in water in a combination or condition which will combine with the tarnishing gases in the atmosphere accessible to the silverware wrapped therein.

3. A fabric for protecting silverware from tarnish comprising a material suitable for wrapping, impregnated with an insoluble compound of silver in a combination or condition which will combine with the tarnishing gases in the atmosphere accessible to the silverware wrapped therein.

4:. A fabric for protecting silverware from tarnish comprising a material suitable for wrap ing, impregnated with oxide of silver.

5. package for silverware having in combination an exterior casing and a series of bags impregnated with a silver constituent in finely divided form which will combine with the tarnishing gases in the atmosphere in contact with them.

6. A package for silverware having in combination an exterior casing and a series of bags impregnated with a silver constituent insoluble in water in finely divided form which will combine with the tarnishing gases in the atmosphere in contact with them.

7. A package for silverware having in combination an exterior casing and a series of bags impregnated with an insoluble compound of silver in finely divided form which will combine with the tarnishing c3 gases in the atmosphere in contact with them.

8. A package for silverware having in combination an exterior casing and a series of bags impregnated with oxide of silver in C5 finely divided form which combine with the tarnishing gases in the atmosphere in contact'with them.

9. A package for silverware comprising a material suitable and adapted for wrapping the silverware to be protected, impregnated with a silver constituent which will combine with the sulphur atoms in the atmosphere accessible to the silverware wrapped therein.

' 10. A package for silverware comprising a material suitable and adapted for wrapping the silverware to be protected, impregnated with a silver constituent insoluble in water which will combine with the sulphur atoms in the atmosphere accessible to the silverware wrapped therein.

11. A package for silverware comprising a material suitable and adapted for wrapping the silverware to be protected, impregnated with an insoluble compound of silver which will combine with the sulphur atoms in the atmosphere accessible to the silverware wrapped therein.

12. A package for silverware comprising a material suitable and adapted for wrapping the silverware to be protected, impregnated with oxide of silver.

13. The method of protecting silverware from tarnish which consists in wrapping the .silverware in a fabric impregnated with a silver constituent in a finely divided form which will combine with the sulphur atoms in the atmosphere accessible to the silver-v ware.

V 14:. The method of protecting silverware from tarnish .which consists in wrapping the silverware in a fabric impregnated with a silver constituent insoluble in water in a finely divided form which combine with the sulphur atoms in the atmosphere accessible to the silverware.

15. The method of protecting silverware from tarnish which consists in wrapping the silverware in a fabric impregnated with an insoluble compound of silver in a finely divided form which will combine with the sulphur atoms in the atmosphere accessible to the silverware.

16. The method of protecting silverware from tarnish which consists in wrapping the silverware vin a fabric impregnated with oxide of silver in a finely divided form.

17. The method of protecting silverware from tarnish which consists in wrapping the silverware ina fabric impregnated with a substance containing silver .atoms in a form which will combine with the tarnishing gases in the atmosphere accessible to the silverware and prevent them from combining with the silver on the surface of the silverware.

GRIN NELL JONES. 

